This invention relates to a flexible coupling device that can be used with an article of knock-down furniture that can be easily assembled by the end-user.
Articles of furniture that consist of several pieces, each capable of rotation relative to each other, are well known. A typical example is the folding chair. One type of folding chair, known as "knock-down" furniture, has several pieces making up the seat, back and legs of the chair. In a typical design, each piece has a bore through which a metal rod is passed. Each piece is strung on this rod like beads on a string until the full complement of pieces has been reached to create a portion of the chair. The pieces are held in place on the rod by some fastening means at the ends of the rod. When the article of furniture is completely assembled, each portion of the chair is capable of rotation relative to each other, thereby allowing the knock-down chair to fold out into an open position for use, or to fold into a closed compact position suitable for storage.
When the article of furniture has some contour to its seat or back portions, the metal rod has been replaced by metal wire, such as 12 gauge fence wire. The flexibility of the wire allows it to conform to this contour. This transverse flexibility is necessary when the contoured article of furniture is folded into its closed position. The wire is typically bent at the ends and driven back into the end pieces. A knock-down chair of this design usually has to be assembled by the manufacturer because the procedure and tools required are beyond the means of the average consumer. Even when assembled by the manufacturer, the wire tends to slowly cut into the furniture material (especially wood) and eventually the chair becomes loose and wobbly.
A common problem with most knock-down furniture items is that they are not designed to be easily assembled by the end-user and still retain the high quality of manufacturer assembled furniture. For high quality, durable furniture, pre-assembly of the furniture by the manufacturer is typically required, thereby increasing the production and shipping costs of the item. In addition, the end-user cannot easily adjust the pre-assembled furniture should the item become loose. This invention addresses these problems of ease of assembly, ease of adjustment and cost-effectiveness, by replacing the use of metal rod or metal wire to couple the pieces of an article of knock-down furniture.
U.S. Pat. Nos. 4,743,068 and 4,958,425 each teach a knock-down furniture coupling device that eliminates some of the problems described above. The coupling devices were used to combine pieces at a plurality of hinge arrangements, each hinge arrangement having a first and a second end piece and a selection of pieces sandwiched between these end pieces. An aligned bore extends through each of the plurality of pieces at each of the hinge arrangements. At each of the hinge arrangements a plastic tube is extended through each of the aligned bores. The tube has a length slightly shorter than the effective length of the aligned bore. A hanger bolt is threaded into each end of the plastic tube prior to assembly. A cap nut is threaded onto the exposed threads of each hanger bolt, once the plastic tube has been located within the aligned bore in each of the hinge arrangements. The cap nuts at each end of the plastic tube are in bearing contact with the end pieces, and are tightened against these end pieces in order to place the tube in tension. The furniture pieces are, consequently, held in longitudinal compression between the two cap nuts, while remaining free to rotate about the longitudinal axis of the tube. Each element of the particular article of knock-down furniture, e.g., the seat, back and legs in the case of a chair, is thus combined and interfaced using this tube assembly at each hinge arrangement in such a manner that the article of furniture is fully collapsible in a closed position, and extendable to its normally operative arrangement in an open position.
While this system was a significant advance in the art of flexible coupling devices, over time several problems have been discovered. The present application teaches the solutions to these newly discovered problems.
At temperatures above 90.degree. the nylon hydraulic tubing which was taught in the patents listed above becomes slightly less rigid (it softens) and deforms under pressure. When a heavy person sits on the chair, especially in hot weather, over time the chair begins to gradually recline beyond the maximum point of recline. This happens because the tubing deforms under the shearing pressure of the intersecting pieces of the chair (2 long bolts) where the back assembly meets the seat assembly.
While a solid rod rather than tubing would be an improvement (greater shearing resistance) it is considerably more expensive and also more cumbersome to use (it comes in 10 to 20 ft lengths whereas the tubing comes in 500 ft rolls). Plus each end of the rod would need to be precisely drilled for later insertion of the lag bolts, thus increasing production costs and making the end product more expensive.
The object of the present invention is to provide coupling device that is a simple solution to these problems and increases the durability of the furniture without adding significantly to the cost of production.